The 3 1/2-hr. conference call brought together nearly two dozen of the nation's best minds on the subject of air quality--and many of them were steamed. As the scientists of the Environmental Protection Agency's Clean Air Scientific Advisory Committee, they are rarely overruled on their recommendations about how the government should react to the latest and best research on the dangers of dirty air. Seven months ago, they warned the EPA in a letter that unless it made at least modest reductions in the amount of airborne soot, thousands of Americans would die prematurely each year. But last December, EPA Administrator Stephen Johnson, citing "the best available science," ignored their counsel. On the phone call last week, an exasperated Dr. James Crapo, professor of medicine at Denver's National Jewish Medical and Research Center, told his fellow scientists, "We need to write another letter and this time take a stronger stand."

Starting when he was a presidential candidate in 2000, George W. Bush has often assured voters that his policymaking would be guided by "sound science." Last week, in his State of the Union address, the President pointed to scientific research as the way to "lead the world in opportunity and innovation for decades to come." Yet growing numbers of researchers, both in and out of government, say their findings--on pollution, climate change, reproductive health, stem-cell research and other areas in which science often finds itself at odds with religious, ideological or corporate interests--are being discounted, distorted or quashed by Bush Administration appointees.

White House officials don't see that pattern of interference. "This Administration has been very supportive of science," Bush's science adviser and respected physicist John Marburger told TIME. "The President wants us to do it right, and doesn't want us to do things that contradict the laws of nature." But in the past two years, the Union of Concerned Scientists has collected the signatures of more than 8,000 scientists--including 49 Nobel laureates, 63 National Medal of Science recipients and 171 members of the National Academies--who accuse the Administration of an unprecedented level of political intrusion into their world. "There have always been isolated incidents where people have played politics with science," says Francesca Grifo, director of the group's Scientific Integrity Program. "What's new is its pervasive and systemic nature. We get calls every week from federal scientists reporting stuff to us."

Rarely, however, are they willing to put their jobs and their research grants at risk by going public with their complaints. That's why it was so remarkable when one of the government's leading experts on climate change, 29-year NASA veteran James Hansen, who is director of the Goddard Institute for Space Studies, charged on the front page of the New York Times that he has been muzzled by the agency. He accused the agency of demanding to review his lectures, papers and postings to the NASA website, as well as screen his media interviews.